The overall objective of this study is to test the fundamental hypothesis of conformal radiation therapy applied to cancer of the prostate: tumor control in locally advanced cancer of the prostate can be increased by using conformal radiation therapy techniques that allow higher tumor doses while maintaining an acceptable level of normal tissue morbidity. To effect a study of sufficient statistical power requires a cooperative multi-institutional approach characterized by greater technical demands and coordination than is customary in clinical trials. To satisfy the more rigorous demands of a cooperative study in conformal radiation therapy, the following specific aims must be accomplished: 1. The development of a consensus definition of "conformal" for prostate treatment, To achieve a uniform definition of "dose to target volume", a consensus regarding the definition of the margin around the tumor must be achieved so that all participating institutions will respect the same definition of "conformal." This in turn requires a preliminary study statistically assessing tumor location, patient immobilization, set-up variations, patient motion, machine output uncertainties, variations in machine parameters, and the effect these variations have on the dose distribution. 2. The development of sensitive criteria for measuring normal tissue morbidity, It is imperative that the normal tissue morbidity not be increased by the higher doses that may be achievable with the conformal techniques. Consequently, sensitive measures of normal tissue response that provide statistically powerful detection of differences between conformal and conventional treatment will be developed. This tool will be tested during the above preliminary study on precision of treatment delivery and evaluated concurrently for patients under conventional treatment. Emphasis will be placed on identifying early indicators of late complications. 3. The evaluation of conformal radiation treatment. Using estimates of rates of tumor control and normal tissue morbidity available from the literature and the experience of participating institutions, a clinical dose escalation trial will be designed and performed in a multi-institutional setting that will test the fundamental hypothesis of conformal radiation therapy. 4. The optimization of conformal radiation treatment of the prostate, Using the dose response data gathered as part of these studies, computer algorithms will be implemented that minimize the expected morbidity of treatment, including themorbidity of failing to control the tumor. This algorithm will account both for the probability of a given injury as well as the morbidity of that injury. 5. The dissemination of results. So that the community at large can take advantage of the results of this study in treatment of the all patients, techniques and versions of conformal therapy will be developed that will Ix appropriate for institutions without highly specialized equipment who perform 80% of the treatment of the radiation treatment of prostate cancer in the United States.